1. Field of the Invention
This invention relates generally to generally to wireless telephony and in particular to a call forwarding feature for wireless telephones that is triggered when the received signal strength at the wireless telephone falls below a threshold level, indicating that the wireless telephone is moving out of service coverage.
2. Description of Related Art
Cellular wireless, like other forms of wireless communication, is an increasingly popular means of personal communication in the modern world. People are using cellular wireless networks for the exchange of voice and data over cellular telephones, Personal Digital Assistants (“PDAs”), cellular telephone modems, and other devices. In principle, a user can seek information over the Internet or call anyone over a Public Switched Telephone Network (“PSTN”) from any place inside the coverage area of the cellular wireless network.
In a typical cellular wireless system, an area is divided geographically into a number of cell sites, each defined by a radio frequency (“RF”) radiation pattern from a respective base transceiver station (“BTS”) antenna. Each BTS antenna in a cell is in turn coupled with a base station controller (“BSC”), cooperatively defining a base station system. The BSC is then coupled to or functionally integrated within a switch (e.g., a mobile switching center (“MSC”)) and/or gateway (e.g., a packet data serving node (“PDSN”)) that provides connectivity with a transport network such as the PSTN (public switched telephone network) or a public or private Internet Protocol network (e.g., the Internet). This combination of network elements is referred to herein as a “serving system.”
When a mobile station, such as a cellular telephone, pager, or appropriately equipped portable computer, for instance, is positioned in a cell, the mobile station communicates via an RF air interface with the BTS antenna of the cell. Consequently, a communication can be established between the mobile station and another entity on the transport network, via the air interface, the BTS, the BSC and the switch or gateway. Such a communication may be referred to as a “call,” whether the communication is a traditional voice “call” or a more advanced data session.
A typical telecommunication system service provider (e.g., Sprint or Verizon) may operate a central controller, such as a service control point (SCP), that assists in call processing. Applying well-known “intelligent network” principles, for instance, a serving system may automatically signal to the central controller when a request is made to connect a call to or from a subscriber via the serving system. The central controller may then apply service logic and send a response to the serving system, instructing the serving system how to handle the call or simply ending the transaction.
A service provider typically maintains an account for each subscriber that it serves, in order to define service authorizations for the subscriber and to facilitate billing. Usually, each subscriber account will have a corresponding service profile that indicates the scope of service to be provided, and the service provider will refer to the profile when serving the subscriber, in order to determine what services to provide or not to provide.
In a telephone system, for instance, a subscriber's profile may indicate how the service provider should handle or respond to attempts to connect telephone calls to or from a given subscriber. For example, the subscriber's profile may indicate that the subscriber is not allowed to place calls to certain area codes, and so the service provider may block any attempt by the subscriber to place calls to those area codes. As another example, the subscriber's profile may indicate that some or all calls to the subscriber should be forwarded to another number or to voice mail under certain conditions, and so the service provider may accordingly forward an incoming call under those conditions.
Typically, each subscriber account will have a corresponding account number or other account identifier, and the account profile will be keyed to that number or other identifier. For example, in a landline telephone system, each customer's account has a directory number that is assigned to the telephone line extending to the customer's premises. A telephone company may then maintain a service profile for each account, keyed to the assigned directory number. When the telephone company processes calls to or from a given directory number, the company may then refer to the service profile that is keyed to that directory number.
As another example, in a mobile telephone system, each mobile phone typically has an assigned identifier (e.g., a mobile directory number (MDN), a mobile identification number (MIN) or mobile station identifier (MSID)). A wireless carrier may then maintain a service profile for each mobile phone, keyed to the assigned identifier. And when the wireless carrier processes calls to or from a given mobile phone, the carrier may then refer to the service profile that is keyed to the mobile phone's identifier.
A service provider can maintain its subscribers' service profiles in various locations. For example, the service provider could maintain the profiles within the serving systems that serve the subscribers, such as in a local switching office for instance. The service profile for a landline subscriber could regularly reside in the serving system that provides the telephone line for the subscriber. The service profile for a mobile subscriber could be downloaded to the serving system from a home location register (HLR) when the mobile subscriber is operating in the serving system. When the serving system receives a request to set up a call to or from a given subscriber, the serving system may then refer to the profile for that subscriber to determine how to process the request.
Additionally or alternatively, a service provider can maintain its subscribers' service profiles in a central controller, such as an SCP for instance. When a serving system receives a request to set up a call to or from a subscriber that it serves, the serving system may encounter an intelligent network trigger and responsively signal to the central controller. The central controller may then refer to the profile for that subscriber to determine how to proceed and may then instruct the serving system accordingly.
Certain services defined by a subscriber's service profile may be configurable. For example, a subscriber's profile may define a call-forwarding service as described above, and the subscriber may be allowed to set the forward-to number and to turn call-forwarding on or off at will. As another example, a subscriber profile may define a voice mail service, and the subscriber may be allowed to turn the service on or off.
To allow subscribers to configure services in their service profiles, the industry has for many years employed a concept known as “feature codes.” A service provider may define specific digit sequences for use in activating, deactivating or modifying particular service features. Each sequence is known as a feature code (or, equivalently, a feature code string). A feature code usually consists of a preceding asterisk (*) or double asterisk (**) followed by a series of numeric digits (0 through 9), but could take other forms as well. Further, a pound sign (#) is sometimes used to delimit particular sequences of digits. For instance, the feature code string                *72 4085550303#        
could mean that a call forwarding forward-to number is being registered. In this example, *72 may indicate that the call-forwarding feature is being accessed, and the digit sequence 4085550303 may indicate the forward-to number.
When a subscriber sends a feature code to a serving system, the serving system may respond to the feature code by employing logic to change (i.e., activate, deactivate or modify) a service feature in a local copy of the subscriber's profile. Alternatively or additionally, the serving system may forward the dialed digits to a central controller, and the central controller may then respond to the feature code by activating, deactivating or modifying a service feature in the subscriber's profile and then sending a response message to the serving system.
Communications between the mobile station and the BTS will typically suffer from varying levels of interference and signal degradation, due to factors such as (i) the number and power level of mobile stations concurrently communicating over the air interface, (ii) obstructions such as buildings, land or foliage, and (iii) the distance between the mobile station and the BTS. Consequently, the strength of RF signals that the mobile station receives from the BTS can vary. Furthermore, the strength of RF signals that the BTS receives from the mobile station can vary.
When a mobile station is actively engaged in a call, if the RF signal strength received by the mobile station and/or BTS becomes too low, the RF link will be effectively cut off, which will thereby disconnect or “drop” the call.
U.S. Pat. No. 6,587,683 describes various feature codes for activating features like call forwarding, call screening, etc. However, the '683 patent does not contemplate initiating of call forwarding when the received signal strength drops below a threshold level or turning off call forwarding when the mobile station re-enters the service network.
U.S. Pat. No. 6,584,316 describes an automatic call-forwarding feature based on the GPS location of the wireless telephone. In particular, if there is a weak signal and the user has previously indicated that call forwarding should occur if the signal strength becomes weak, the method obtains a current GPS location of the mobile station. A computer program then proceeds to look up a land line telephone directory number stored in the mobile station's memory associated with the mobile station's GPS location. If there is no directory number for the current location, the process is complete and no call forwarding is accomplished. Only if there is a directory number for the GPS location of the mobile station will call forwarding proceed. This method thus requires manual entry of specific call forwarding numbers for particular locations where signal strength is weak. Obviously, this approach has limited usefulness, since it is dependent on a land line telephone being present nearby, and furthermore requires significant operator input to provide the list of landline telephone numbers at various locations.
The present invention provides an improvement to the above referenced patents and provides for automated initiation of call forwarding when signal strength is weak, without regards to the current location of the mobile station, or whether there is a landline telephone with a previously known directory number nearby.